Polymerization of N-vinyl-2-pyrrolidone (vinylpyrrolidone) by free radical mechanisms is well known and is described for instance in U.S. Pat. Nos. 4,058,655, 4,053,696 and 3,862,915. The polymerization is usually carried out in water or organic solvent using free radical initiators such as hydrogen peroxide, alkyl hydroperoxides, dialkyl peroxides such as di-tert.-butyl peroxide or azodiisobutyronitrile. Previously suggested initiators have, however, not been completely satisfactory. It has for instance been necessary to use different initiator systems depending upon whether low, medium, or high molecular weight polyvinylpyrrolidone (PVP) polymer product is desired. While some variation of molecular weight has been possible with previously used initiators, no single initiator has previously been known which could be used for making PVP of a wide range of molecular weights. It has also been difficult with many initiator and solvent systems to obtain polymer of narrow molecular weight range. The toxicity of decomposition products of commonly used initiators has also frequently resulted in product unsuitable for pharmaceutical use. Other disadvantages have included a need for amine or ammonia buffers with hydrogen peroxide to control pH, the production of undesirable impurities as decomposition products of eg. azodiisobutyronitrile initiator, etc. Previously used peroxides such as di-tert-butyl peroxide require the use of extremely high temperatures.
The various disadvantages inherent in use of previously known initiators are largely eliminated or alleviated by the process of the present invention.